Olefin polymers have excellent processing characteristics in various processing methods and also have excellent various characteristics such as mechanical properties (e.g., hardness, creep characteristics and abrasion resistance), appearance (e.g., surface gloss and transparency), chemical resistance and heat resistance. Further, the olefin polymers are relatively inexpensive. Accordingly, the olefin polymers have been widely used in the past.
Olefin polymers containing inorganic fillers to improve the stiffness and dimensional stability thereof are also widely used.
However, the olefin polymers have the disadvantages as compared to other amorphous resins such as styrene resins in the suitability for secondary processings such as vacuum forming and pressure forming which shape sheets obtained by, for example, extrusion molding into various shapes. For example, due to a large degree of sagging of a semi-molten sheet in the heating step, the sheet sagged contacts a heater to occur troubles, the producibility is poor due to a long heating time required for heating, and the molding condition ranges for shaping with a uniform thickness distribution are so narrow that use of the conventional vacuum forming machine is difficult. Thus, although the olefin polymers have various advantages described above, those cannot be used in some cases.
Japanese Patent Application (OPI) No. 28144/82 (published unexamined Japanese Patent Application) discloses blending a styrene resin with a polypropylene resin as the olefin polymer using a thermoplastic styrene block copolymer rubber as a compatibilizer. This method, however, has the following disadvantages. The impact resistance is improved as the amount of the styrene block copolymer rubber as a compatibilizer added increases, but the stiffness rapidly deteriorates. Even if an inorganic filler is added to supplement the deterioration, the stiffness is improved but the impact resistance rapidly deteriorates. As a result, the thermoplastic styrene block copolymer rubber must be further added to supplement the deterioration of the impact resistance, resulting in deterioration of the stiffness. Thus, good balance between stiffness and impact resistance cannot be obtained.
Therefore, with respect to the stiffness and impact resistance of the product shaped by this method, if the impact resistance is predominantly improved, deterioration of the stiffness is unavoidable. Further, with respect to the thermoforming property, improvement can be obtained as compared to a sheet obtained from an olefin polymer alone, but the molding condition ranges for shaping with a uniform thickness distribution are narrow and the heating time required for shaping is too long. Thus, the above method is practically unsatisfactory.